The disclosure concerns a sensor subassembly for a vehicle, and a device for measuring rotational movements of a wheel bearing for a vehicle.
In the prior art, rotation speed sensors with integral bearing cap are used to measure the wheel rotation speed and seal the wheel bearing media-tight, at present as a metal cap or a plastic cap with integral metal ring and sensor unit. The bearing interface and bearing are sealed in metal caps by force fit, i.e. by a press seat, in conjunction with an organic coating which compensates for micro-leakage paths in the press joint. The coating is usually applied by cathodic dip coating (CDC).
Plastic caps are currently structured so that a sealing element applied externally and compressed axially, such as for example an O-ring seal or a spray-molded seal of silicon or similar, seals the wheel bearing media-tight and at the same time by its elasticity compensates for the different thermal expansion coefficients of the various materials, in particular when plastics and metals are used.
Publication DE 10 2005 015 261 A1 and patent specifications U.S. Pat. No. 6,218,827 B1 and U.S. Pat. No. 5,814,984 each describe a device for measuring rotational movements of a wheel bearing, in particular the wheel bearing of a motor vehicle. The device described comprises a signal emitter arranged on a rotating part of the wheel bearing and a stationary sensor subassembly with a retaining ring and a cap-shaped plastic part as a cover for the wheel bearing. The sensor subassembly is here fixed and the wheel bearing sealed such that the cap-shaped plastic part and the retaining ring are compressed with introduction of a seal onto the stationary part of the wheel bearing.
For sensor assemblies with plastic caps, according to the prior art described above it must be ensured that in the case of axial compression, the compensating and sealing element must seal two leakage paths simultaneously. These are a first leakage path along the integral retaining ring into the plastic cap and hence on an indirect route into the wheel bearing, and a second leakage path along the integral retaining ring directly into the bearing. Here because of the axial compression, for different bearing lead-in chamfers, the sealing concept must be designed afresh each time in order to guarantee the seal by standardized compression of the sealing element, which constitutes a disadvantage of the known solutions. By adapting the sensor encapsulation to the wheel bearing, the abovementioned interface for the compensation and sealing element must likewise furthermore be designed afresh and evaluated or tested for each wheel bearing.